The top metal layer of a LCD-on-silicon display pixel serves both as a mirror to reflect light and as an electrode to control the gray scale of the top LCD material. Aluminum (Al) is normally used because of its high reflectivity and its compatibility to integrated circuit production. If the aluminum layer is thick ( greater than 2000 xc3x85), then the grain size is normally big which degrades reflectivity. If the aluminum layer is thin ( less than 2000 xc3x85), then light penetrates through the aluminum layer and affects the functioning of the transistor below by the photoelectric effect. Also, the via, which serves as the electrical connection to the top metal pixels, usually produces a dimple on the aluminum layer which also affects reflectivity.
U.S. Pat. No. 5,486,485 to Kim et al. describes a method of forming a plurality of SOI (silicon-on-insulator) transistors in a pattern beneath planarized reflective surfaces of a reflective display.
U.S. Pat. No. 5,946,547 to Kim et al. describes a method of fabricating LCD devices using three patterning steps. When reflective-type LCD devices are fabricated, a reflective layer comprised of Al, for example, may be formed on the rear surface of the substrate opposite the patterned conductive layer to prevent loss of light which penetrates through the pixel electrode.
U.S. Pat. No. 5,633,182 to Miyawaki et al. describes a method of manufacturing an image display device wherein the switching (driving) transistor and the interconnection layer are formed on one of the surfaces of the insulating layer (insulator) which is remote from the liquid crystal layer while the liquid crystal voltage applying electrode is formed on the other surface of the insulating layer close to the liquid crystal layer. Thus it is possible to provide a light-blocking layer near the transistor allowing the aperture ratio to be increased, reducing the cross-talk among the adjacent pixels, and increasing the S/N ratio.
U.S. Pat. No. 5,471,330 to Sarma describes a liquid crystal display pixel and a method of forming same, wherein each pixel has a thin film transistor with a silicon pixel electrode. A doping and recrystallization of the silicon is effected to increase the electrical conductivity and light transmittance of the silicon adequately for the pixel electrode. An ITO (indium tin oxide) layer is not required for the pixel electrode.
Accordingly, it is an object of the present invention to provide LCD-on-silicon pixels and a method of fabricating LCD-on-silicon pixels using a thin aluminum layer.
Another object of the present invention is to provide LCD-on-silicon pixels and a method of fabricating LCD-on-silicon pixels having a planar upper surface unaffected by any defects in the underlying via.
A further object of the present invention is to provide LCD-on-silicon pixels and a method of fabricating LCD-on-silicon pixels with increased reflectivity of the aluminum mirror by depositing a thin aluminum layer with small grain.
Yet another object of the present invention is to provide LCD-on-silicon pixels and a method of fabricating LCD-on-silicon pixels that prevent light penetrating the aluminum mirror layer and affecting the underlying transistor junctions by photoelectric effect.
Another object of the present invention is to provide LCD-on-silicon pixels and a method of fabricating LCD-on-silicon pixels that permit an increase in the permissible amount of light to fall on the pixels so as to have a larger and/or clearer overall picture/images.
Other objects will appear hereinafter.
It has now been discovered that the above and other objects of the present invention may be accomplished in the following manner. Specifically, a substrate having an upper layer of silicon is provided. A via is formed in the silicon layer. An opaque conducting layer is deposited over the silicon layer, filling the via. The opaque conducting layer is planarized and a reflective layer is deposited over the opaque conducting layer to form an LCD-on-silicon pixel device. Alternatively, the via may be formed by a deposition and etch back process with one metal. An opaque conducting layer is then deposited and planarized before deposition of the reflective layer. An LCD-on-silicon pixel device, comprises a substrate having an upper silicon layer. The upper silicon layer has a plug therein comprised of an opaque conducting material. Over the upper silicon layer and the opaque conducting plug is a planar opaque conducting layer and a planar reflective layer is over the planar opaque conducting layer.